Mixed and hypermetropic astigmatism proves to be the most commonly encountered eye disease in humans, which has both natural and post-operative origin. A number of surgical techniques have been suggested up till now for treatment of mixed and hypermetropic astigmatism of which the so-called thermocoagulation methods have gained the most extensive application. The essence of such methods resides in that some cornea areas are exposed to the effect of elevated temperature with the aid of a needle penetrating into the cornea by 40 to 50 .mu.m, the temperature at the needle point being within 100.degree. and 200.degree. C. As a result of such a thermal effect there occurs structural alteration of the cornea and hence redistribution of stresses therein, which should result, with appropriately selected thermocoagulation zones, in elimination of mixed and hypermetropic astigmatism in patients operated upon.
Thus, for instance, one prior-art method for surgical correction of astigmatism is known to provide local thermocoagulation (cf.. e.g., V. B. Gudechkov, the paper "Keratocoagulation in surgical correction of astigmatism" in: Collected proceedings of the Moscow research institute for microsurgery of the eye, Moscow, 1981, pp. 78-83 (in Russian). When carrying said method into effect first one should find, using any known technique, the position of an optically weak meridian known as the meridian of the minimum refractive power. Then point coagulation is carried out on the diametrally opposite, with respect to the central optical zone, sides on the area of the optically weak meridian, the coagulation points being spaced along a circumference having, as a rule, a diameter of 6 mm. However, the aforesaid method suffers from a number of substantial disadvantages concerned with the onset of nonuniform zonal corneal stresses and hence post-operative complications in the course of cicatrization. In particular, the method is fraught with the formation of stresses in the optically weak meridian and may also lead to corneal deformation, which to a considerable extent affects the efficacy of such a surgery and is frequently accompanied by relapses of astigmatism.
Another prior-art method for surgical correction of hypermetropic astigmatism, according to S. N. Fyodorov and V. B. Gudechkov (SU, A, 1,090,385) is known to provide preliminary marking-out of the cornea, wherein the optic centre of the eyeball and the central optic zone are first found out, followed by radial marking-out of the cornea from the optic zone towards the corneal periphery along four meridians. Marking-out over, point coagulation is carried out along said radial directions, using a needle heated up to 100.degree. or 200.degree. C. and applied for 0.3 to 0.5 sec. As practical experience shows such a radial arrangement of the coagulation points results, however, in inadequate corneal deformation, which is accompanied, on the one hand, by higher refraction in all the four meridians, and on the other hand, leads to relapses of astigmatism.